In the past, it has been customary to form glass articles by various known methods including pressing, blowing, spinning, or vacuum forming molten glass into a desired configuration. The conventional press and blow and blow and blow processes are generally limited to the formation of hollow articles and require rather complex apparatus and multiple process operations. Standard gob pressing procedures permit the pressing of a variety of glass articles, however, due to the mass of the molten glass gob which must be distributed during the pressing and the inherent cooling of the glass due to the residence contact time between the mold and the plunger, the thinness to which such articles can be pressed without detrimental surface defects and checking is severely limited.
Vacuum forming has the advantage of not only being able to form articles from laminated sheet material, but also the ability to form relatively thin articles. However, in normal vacuum forming processes, the upper surface of the article being formed follows the contour of the bottom of the article in contact with the mold surface, such that any changes in the contour of the bottom of the article are reproduced on the top surface thereof whether or not desired. Thus, it is not possible to form footed articles such as plates which may be stacked with a standoff, in view of the fact that the upper surface of the plate would follow the contour of the foot formed in the bottom of the plate, thus disrupting the plate surface. Vacuum forming of sheet material also precludes the provision of crisp or sharp blends of angled surface intersections, since the upper surface of the sheet which is not in contact with the sharp demarcation provided in the mold surface, will merely form a radius at such intersection, independent of the sharp section which may be formed on the bottom surface which is in contact with the mold. Accordingly, it is virtually impossible to vacuum form an embossed surface with any discernable clarity in the upper surface of a vacuum formed article.
Various processes and apparatus may be utilized in the vacuum forming of articles from sheet glass including a horizontal conveyor type of apparatus as shown in U.S. Pat. No. 3,114,620 and a turret or rotary wheel type of apparatus as shown in U.S. Pat. No. 3,231,356. The trimming of such vacuum formed articles is shown in U.S. Pat. Nos. 3,193,367 and 3,582,454, with the latter patent being specifically directed to the trimming of articles vacuum formed from laminated glass sheet.
Although vacuum forming of articles from glass sheet, whether of a unitary or laminated construction, has been known in the past, it has been a principal object of the present invention to provide method and apparatus for improving upon the vacuum forming of articles from sheet glass by incorporating the pressing of the sheet while still in a molten condition and thereby facilitate the formation of thinly pressed articles with controlled upper and lower surface contours of desired configuration.